In the execution of particular work with single-cylinder knitting machines or hosiery knitting machines, such as for example for forming relief patterns obtained by means of toweling-stitch work, there is a requirement to be able to select the sinkers individually, so as to actuate contiguous sinkers in different manners in order to form stitches of the toweling type only with some needles, differently from contiguous needles, which instead form non-toweling stitches.
Selection devices that require the use of particular sinkers, different from conventional sinkers, are currently used to meet this requirement.
More particularly, one of these selection devices uses sinkers provided with a substantially L-shaped body, in which one arm of the L-shape constitutes the shank of the sinker and the other arm of the L-shape is arranged on the outer side of the sinker ring and is provided with a selection tooth. Said selection tooth can be engaged or not by a selection actuator, which laterally faces the sinker ring so as to produce a diversified actuation of the sinker along the corresponding radial slot of the sinker ring in which it is accommodated, depending on whether one wishes said sinker to cooperate with the needles in forming a toweling stitch or to cooperate with the needles in order to form another stitch.
Another type of sinker selection device requires the use of sinkers that can oscillate on a radial plane with respect to the sinker ring. Said sinkers are generally provided, on their side that is directed toward the bottom of the corresponding radial slot of the sinker ring, with a selection tooth, which protrudes downwardly from the sinker ring and which, depending on the selection requirements, is contacted or not by a selection actuator that faces the sinker ring in a downward region. If the selection tooth is contacted by the selection actuator, the corresponding sinker undergoes an upward oscillation, which makes it engage sinker actuation cams supported by the sinker cap, which faces the sinker ring in an upward region; said sinkers cause the diversified actuation of the sinker with respect to the actuation performed by means of other cams that engage the sinker when it is not raised, i.e., when the selection actuator does not act on the selection tooth. In in this manner also, the diversified actuation of the sinker allows to actuate the sinker so that it must cooperate with the needles of the to machine in forming toweling stitches or in the forming of other stitches.
These sinker selection devices have the drawback of requiring special sinkers, which have a higher cost than conventional types of sinker. As sinkers are elements of the machine that need to be replaced periodically, having to use special sinkers affects the operating costs of the machine.
Moreover, in the case of devices that require the use of special oscillating sinkers, there are problems in controlling the sinkers when the machine operates at high actuation speeds. In this type of device there are also problems in positioning the selection actuator below the sinker ring, in a region of the machine that is generally already occupied by many other elements required for its operation.